The present invention relates to a system for smoothing or spreading transitions between image regions included in television signals. The signals to be transmitted are processed in a still picture signal processing method and in a motion picture signal processing method. Particularly, the present invention is a circuit for accurately detecting a motion signal which represents a moving image so as to control the transitions between image regions of a frequency-unfolded image signal.
Standard television systems such as an NTSC or a PAL system, processes a television signal adaptively in accordance with an amount of motion in the signal. This adaptive processing of the signal may result in some quasi-motion picture regions between image regions being processed in a still picture signal processing method and other image regions being processed in a motion picture signal processing method. If differences in the processing methods are used, the different regions and the transition between them can be discerned by a viewer; therefore, image quality is degraded.
For example, for the purpose of separating chrominance and luminance components from a composite video signal, a frame comb filter or a line comb filter may be used. As long as there is no change in the image signal at frame time intervals, chrominance and luminance components from the composite video signal can be completely separated using the frame comb filter, the completely separated. If the scene changes, over the frame time intervals, then some color information will be present in the separated luminance component, and some brightness information will be present in the chrominance component.
A line comb filter, also used to separate the luminance and chrominance components from the composite video signal does not produce significantly degraded component signals in the presence of image motion. However, the line comb filter reduces the vertical resolution of the reproduced image in comparison with the frame comb filter. In addition, in locations where a vertical transition occurs, an image processed by the line comb filter may be degraded due to both color information introduced into the luminance component, producing an image artifact known as hanging dots and brightness information introduced into the chrominance, producing incorrect colors in the neighborhood of the transition.
Therefore the television signal is adaptively processed by detecting the presence or absence of image motion. In the regions in which the image is stationary, the frame comb filter is used, and in the regions in which the image is moving, the line comb filter is used.
Yet another example of such adaptive processing is an adaptive double-scanned, non-interlaced scan converter. In such a converter, inter-stitial lines are displayed between lines of the current field. The inter-stitial lines however, may be those transferred from the preceding field, in the presence of image changes producing visible artifacts such as serrated contours. The inter-stitial lines may also be interpolated from lines within the current field, but the vertical resolution is reduced and line flicker may occur. In regions in which image changes are detected, intrafield interpolated interstitial lines are displayed and field-delayed interstitial lines are displayed in other way.
Yet another example is an adaptive peaking circuitry in which regions having relatively high noise are processed with a relatively low peaking factor and regions having relatively low noise are processed with a relatively high peaking factor.
In the above examples, the television signals are processed adaptively in response to the values of estimated parameters of the image. The parameters are motion, in the case of luminance/chrominance separation and are double scanning non-interlaced conversion, and a relative level of noise, in the case of the peaking. Differently processed regions, and noticeable boundaries between regions where the parameter is present and those where it is absent are undesirable artifacts introduced by the above types of adaptive processing types.
U.S. patent application for the invention entitled "An Improved Video Signal Recording System" earlier filed in the United States Patent & Trademark Office on Aug. 17, 1990 by SamSung Electronics Co., Ltd., and duly assigned Ser. No. 07/569,029, describes a recording system for recording and reproducing a full bandwidth video signal on and from a recording medium having a limited bandwidth by folding the high frequency component of a luminance signal into the low frequency component of the luminance signal.
In the U.S. patent application Ser. No. 07/569029, a motion signal which represents a moving image is recorded together with the folded luminance signal and the chrominance signal on the recording medium. The motion signal is used to control the transition between regions of the full bandwidth luminance signal which is unfolded into the original frequency bands during reproduction.
In the inventions described in the foregoing paragraphs, the high frequency component of the luminance signal is folded into the low frequency component of the luminance signal in recording. At this time, the high frequency component of the luminance signal is modulated by a folding carrier, so that the folded luminance signal has a phase difference of 180 degrees between frames, between scanning lines, and between pixels.
Accordingly, in reproducing, the high frequency component folded into the low frequency component of the folded luminance signal is demodulated by the unfolding carrier having the same phase and frequency as those of the folding carrier, so that the high frequency component of the luminance signal is unfolded into the original frequency band.
However, the folding carrier and the side band thereof will be present in the unfolded luminance signal. The resultant luminance signa.1 unfolded by the folding carrier and the sidebands thereof has a phase difference of 180 degrees between frames.
As a result, the conventional motion signal detecting circuit, for detecting the level difference of pixels between frames as the motion signal, has difficulty detecting accurately the motion signal, from the unfolded luminance signal due to the phase off-set between frames.
The Korean patent application No. 90-18737 on the invention entitled "A Motion Signal Detecting Circuit", filed on Nov. 19, 1990, by Ko, describes techniques, for eliminating the folding carrier and sidebands thereof, contained in the unfolded luminance signal by a prefilter and for detecting a motion signal through filtering, by means of a comb filter, the unfolded luminance signal in which the folding carrier and the sidebands are eliminated.
This prefilter can however, eliminate the folding carrier and sidebands therefore contained in the unfolded luminance signal of the vertical and horizontal direction having a large correlation. It is difficult to completely eliminate the folding carrier and sidebands thereof contained in the unfolded luminance signal from the diagonal direction, that is, the temporal direction having a small correlation.
Therefore, since the unfolded luminance signal, which is output from the prefilter has a phase difference of 180 degrees by the folding carrier sidebands remaining in the diagonal signal component, it is difficult to derive an accurate value for the diagonal direction of the motion signal being the difference component between frames detected by the comb filter.